The present invention relates to depth-type oil filters particularly adapted for the filtration of motor vehicle engine oil. In the art of motor vehicle engine oil filtration, it has long been recognized that the flow characteristics of the oil to be filtered does not remain uniform. The variations in engine temperature affect the viscosity of the oil. Also, the dirt and dust particles that find their way into the lubrication system are not of uniform size. The flow rate of a depth-type filter having a filter media of uniform porosity varies with the viscosity and degree of contamination of the oil to be filtered. To compensate for these variables so that a substantially uniform flow rate is maintained through the filter, the prior art suggests that the filter be constructed and arranged to permit parallel, dual or multi-flow rates through the media.
As disclosed in U.S. Pat. No. 2,559,267, issued July 3, 1951 to C. A. Winslow et al. for "Filter" or U.S. Pat. No. 3,562,895 issued Feb. 16, 1971 to L. F. Neibergall et al for "A Method of Making Filter", this may be accomplished by axially stacking depth-type filter media in an oil filter cartridge to provide a dual flow automotive type oil filter. This may also be accomplished by arranging a uniform porosity filter media so that it permits two-path depth-type filtration by having the oil pass through different radial thicknesses of the filter media. Reference may be made to U.S. Pat. No. 3,468,425, issued Sept. 23, 1969 to A. H. Engstrom for a "Fluid Filter Element" for an example of this construction.
It is an object of the present invention to provide a simple filter construction of the depth-type in which the filter media is a uniform porosity material which is externally influenced to provide dual or multi-flow filtration.